The present invention relates to a liquid crystal display (LCD) device for use in the optical display and the manufacturing method therefor, and more particularly, to an LCD device for strengthening the support structure of the insulation layer partitioning the liquid crystal layer and the manufacturing method therefor.
The liquid crystal display (LCD) device can operate by relatively low driving voltages, so as to conserve a little electric power. Also, it is thin and has a simple structure like a plasma display panel or electrical field light emitting effect device. Therefore, LCD devices have made significant advances in development as a picture display device in a wide variety of diversified fields, and the expansion of applications is continuing.
Since a currently utilized liquid crystal display device of an active matrix type using a simple X-Y matrix or thin-film transistor (TFT) is a twisted nematic (TN) type or super-twisted nematic (STN) type, a polarized plate for controlling light is required. However, the polarized plate in the LCD intercepts more than 50% of the emitted light while controlling the light polarization. Accordingly, efficiency in the use of light is reduced.
For this reason, a background light source having a considerable brightness is required to obtain an image having a desired brightness. Thus, in the case of a laptop wordprocessor or computer which uses a dry cell battery or an accumulative battery cell as a power supply source, extended use is limited due to the excessive power consumption of the background light source.
Also, in the general LCD including the TN and STN liquid crystals, since liquid crystal is filled between two glass plates, it is necessary for a cell gap which is a light-controlled area to be strictly adjusted in order to form a uniform picture image. However, due to current technological limitations in the manufacturing of the glass plate, the super-enlarging of an LCD panel is difficult to achieve.
Taking the above-described problems into consideration, it is necessary to decrease the burden of cell gap adjustment by enhancing the efficiency of the use of light with the removal of the polarizing panels and using a pair of substrates.
Examples of the conventional liquid display devices not using the polarized plate, include a cholesteric nematic transition (CNT) type which uses a phase transition effect and a dynamic scattering mode (DSM) type which was devised during early LCD development. The DSM type LCD exhibits a slow response time and is thicker than other LCD devices, so that it is no longer in common use.
Also, another example of an LCD not using a polarized plate to increase the efficiency of light is a polymer-dispersed liquid crystal display (PDLCD). However, since the PDLCD is made of a polymer material more than half of whose volume is light-transmitting, the scattering of light should be enough brought about to obtain a clear contrast. To attain these requirements, there is a structural limitation in that the thickness of the liquid crystal layer should be at least 20 .mu.m.
An LCD which adopts an electrical field effect type liquid crystal having a new structure in which the above conventional problems of the LCD are considerably improved, was filed on May 8, 1992 as Japanese patent application No. hei 4-116146 of which the corresponding U.S. patent application was filed on May 10, 1993. A continuation-in-part application of the above U.S. patent application has been filed on Aug. 24, 1993 (whose serial number has yet to be delivered).
The above LCD has a fast driving speed and high light-utilization efficiency, in which the liquid crystal layer provided between the opposing electrodes is isolated by a plurality of insulation layers to form a multi-layer structure, the polarized plate is not used and only a single sheet of a glass substrate is applied. Here, a function layer for controlling the light is formed by deposition on the top of the resultant.
That is, as shown in FIG. 1, field effect type liquid crystal layers 22 are arranged between two opposing electrodes 10 and 18 the interval of which is maintained by the support of the columns 12. Also, insulation layers 20 are arranged for separating liquid crystal layers 22 into multiple layers. Insulation layers 20 are fixed with respect to one another by means of columns 12 which are locally arranged, and has inlet holes 14 for locally injecting the liquid crystal. Here, the thickness of each layer of liquid crystal layers 22 is less than 3 .mu.m, and the thickness of each insulation layer is less than 5 .mu.m. Here, epoxy resin can be used as a material for insulation layer 20. However, metal oxides, more particularly an aluminum oxide, can be used instead.
A method for manufacturing the above-constructed liquid crystal display device will be described hereinafter.
Referring to FIG. 5, a conductive material is deposited on the surface of a black plastic substrate 16, so as to form a predetermined pattern of the lower electrode 18.
Referring to FIG. 6, firstly, on the surface of the substrate, epoxy resin layer 20 and polyvinyl alcohol (PVA) layer 22a are repetitively deposited using a spin coating method or roll coating method. Next, on the topmost epoxy resin layer 20, an indium tin oxide (ITO) is deposited to thereby form a predetermined pattern of the upper electrode 10.
Referring to FIG. 7, a photomask pattern is formed on upper electrode 10 so as to leave a photoresist 24.
Referring to FIG. 8, the portions which are not covered with photoresist 24 are plasma-etched to thereby form wells for forming columns 12. Next, the epoxy resin fills the cavities and is coated on the surface of the lamination structure, so that columns 12 and surface epoxy resin layer 26 are formed.
Referring to FIG. 9, liquid crystal inlet holes 14 are formed by the use of a photomask pattern and plasma etching. Here, water is supplied through inlet holes 14 so that it dissolves and removes all of PVA layers 22a between the insulation layers. Accordingly, the dissolution layer connected to inlet holes 14 is removed, to thereby form cavities 22b which would be filled up with the crystal liquid. At this point, each epoxy resin layer 20 maintains a vertical interval by columns 12 (as shown in FIG. 8) so that cavities 22b are sustained.
Referring to FIG. 10, in a vacuum state, the liquid crystal is spread on all the lamination structure which is previously dried, so that it inflows along the cavities 22b through inlet holes 14 to form a liquid crystal layer 22. Upon the completion of the filling of the liquid crystal, the epoxy resin is coated on the whole surface of the topmost insulation layer so as to seal off inlet holes 14 through which the liquid crystal is injected. Where the blockage of light is necessary, a blinding plate 11 is formed on columns 12 and inlet holes 14 so that a reflective type LCD as shown in FIGS. 1 through 4 is manufactured.
The above-described manufacturing method is restricted wherein a water-soluble PVA is used as the material for dissolution layer for ensuring the cavities in which the liquid crystal is filled up, and an epoxy resin is used as the material for the insulation layer. However, a metal, e.g., aluminum, can be used instead of the water-soluble PVA and a metal oxide can be used instead of the epoxy resin.
When the LCD devices are manufactured according to the above processes, the support structure for the insulation layer using the columns is weak, which makes it difficult to obtain a high quality liquid crystal layer. This is because regardless of how the wells are formed or how the resin is then filled up for forming the columns, the contact plane between the column resin and the insulation layer is thin and is incomplete at some portions so as to be easily separated from each other.